So far, for example, Patent Document 1 discloses a control apparatus for an internal combustion engine including a variable valve operating mechanism which can stop intake valves in a closed state. The conventional control apparatus stops the intake valve in the closed state to prevent fresh air from being introduced into a catalyst when a fuel cut is executed at the time of deceleration, thereby attempting to inhibit the catalyst from being deteriorated.
In addition, for example, Patent Document 2 discloses an internal combustion engine including a positive crankcase ventilation system which circulates blow-by gas in the inside of the engine back to intake air to treat it. FIG. 1 of Patent Document 2 represents a configuration which is provided with a blow-by gas passage, a fresh air introduction passage, a breather passage and a PCV valve by way of example of such a positive crankcase ventilation system.
More specifically, the blow-by gas passage, which allows a crankcase to be communicated with the inside of a head cover, is provided to lead gas that is blown from the combustion chamber side to the crankcase side via a gap between a cylinder and a piston (that is, blow-by gas), into the inside of the head cover. The fresh air introduction passage, which allows an intake passage at the upstream side of a throttle valve to be communicated with the inside of the head cover, is provided to introduce fresh air into the inside of the head cover. The breather passage, which allows the intake passage at the downstream side of the throttle valve to be communicated with the inside of the head cover, is provided to supply the blow-by gas in the inside of the head cover into intake air flowing through the intake passage. Moreover, the PCV valve is a valve for adjusting a flow rate of the blow-by gas circulated back into the intake air via the breather passage.
Including the above-described document, the applicant is aware of the following documents as a related art of the present invention.    [Patent Document 1] Japanese Laid-open Patent Application Publication No. 2007-162506    [Patent Document 2] Japanese Laid-open Patent Application Publication No. 2006-250080    [Patent Document 3] Japanese Laid-open Patent Application Publication No. 7-305646    [Patent Document 4] Japanese Laid-open Patent Application Publication No. 2008-267189